1. Field of the Invention
The present invention generally relates to a semiconductor-processing apparatus, and particularly to a semiconductor-processing apparatus in which a substrate is moved between a reaction area and a transfer area by moving a susceptor up and down.
2. Description of the Related Art
As high integration of semiconductor devices has progressed, ALCVD (Atomic Layer Chemical Vapor Deposition) having better thin film formation controllability than CVD (Chemical Vapor Deposition) has received increased attention.
ALCVD is a thin film formation method for forming a thin film by introducing multiple source gases alternately or in order into a reactor and causing the source gases adsorb to a surface of a semiconductor wafer. In this method, because thin film formation is performed using only an adsorption layer, controlling film formation at a film thickness of several molecules is possible. Additionally, this method demonstrates a satisfactory step coverage characteristic.
When a thin film is formed by ALCVD, evacuating a source gas used until that time from within the reactor is required at the time of source gas switching. If any previously-used source gas remains in the reactor, a CVD reaction may occur in vapor phase, thereby making it difficult to control a film thickness at a molecular layer level. Additionally, fine particles generated by a CVD reaction in vapor phase may cause particle contamination.
If a purge time for eliminating a remaining gas completely from within the reactor lengthens, throughput declines. Given this factor, in conventional semiconductor-processing apparatuses, the inside of the chamber is divided into a reaction area and a transfer area to reduce dead space as well as to shorten the purge time.
Conventional semiconductor-processing apparatuses are configured, for example, as shown in FIG. 11 (e.g., Japanese Patent Laid-open No. 1994-318630).
The semiconductor-processing apparatus shown in FIG. 11 comprises a chamber 100 and a drive portion 200. In the chamber 100, a susceptor 102 for placing a semiconductor wafer 101, which is an object to be processed, on it is provided movably up and down. The drive portion 200 is rotated and driven along with the susceptor 102 moving up and down.
FIG. 11 shows a position in which the susceptor 102 is in a processing position (an ascent position). In this position, the upper surface of the outer peripheral portion of the susceptor 102 contacts the undersurface of the inner circumference of a separation plate (base ring) 103; by this, the inside of the chamber 100 is divided into a reaction area (a reactor) 104 and a transfer area 105.
The susceptor 102 hangs multiple (normally three) lift pins 106 movably up and down. When the susceptor 102 goes down, the lift pins 106 go down together with it. When the lift pins 106 go down together with the susceptor 102 and their lower edges bump into a cradle 107 for supporting use, the lift pins 106 stop going down at that point. Subsequently, when the susceptor 102 further goes down toward a transfer position (a descent position), the lift pins 106 go up relatively to the susceptor 102. As a result, the lift pins 106 lift the semiconductor wafer 101 placed on the susceptor 102 up from the susceptor 102.
The semiconductor wafer 101 lifted up from the susceptor 102 by the lift pins 106 can be carried out of the chamber 100 through an access port 108 by a transfer arm (a manipulator) not shown in the figure.
Additionally, by the actions in reverse order to the above-mentioned, a new semiconductor wafer to be processed next can be introduced into the chamber.
In a conventional semiconductor-processing apparatus, a reaction area and a transfer area are divided by physically contacting a susceptor with a base ring. However, placing the susceptor and the base ring in contact with each other without a gap is exceedingly difficult because it requires, for example, parallelizing contact surfaces of the susceptor and the base ring with precision and so forth. Additionally, in the conventional semiconductor-processing apparatus, because a lift pin is inserted movably up and down into a through-bore formed in the susceptor, a gap exists between the lift pin and the through-bore. Consequently, the conventional semiconductor-processing apparatus has a problem that the reaction area and the transfer area cannot be divided airtightly.
If the reaction area and the transfer area are not divided airtightly, a reaction gas flows into the transfer area from the reaction area; because evacuating the reaction gas having flowed in becomes difficult, a purge time is lengthened. Further, because the reaction gas reacts with a secondly-introduced reaction gas in CVD, particle contamination is caused. Additionally, because a thin film is formed inside the transfer area, a maintenance cycle is shortened.
Although a flow of a reaction gas passing through the gap between the lift pin and the through-bore can be blocked or reduced by reducing the gap, this increases wear debris, thereby causing particle contamination.
Additionally, in the conventional semiconductor-processing apparatus, there is another problem: If a pressure inside the reaction area becomes lower than a pressure inside the transfer area (e.g., when a reaction gas is evacuated), a semiconductor wafer rises being affected by a gas passing through a gap between the lift pin and the susceptor and moves, thereby generating wear dust and causing particle contamination.